Serum vitamin D levels and appendicular skeletal muscle index in United States adolescents: A cross-sectional study based on NHANES.

With the rising prevalence of sarcopenia among adolescents, the relationship between vitamin D levels and appendicular skeletal muscle index (ASMI) in US adolescents aged 8 to 20 years with a body mass index (BMI) of 18.5 kg/m2 or higher remains ambiguous. Data from the National Health and Nutrition Examination Survey (NHANES) conducted between 1999 and 2006 were analyzed, including 6318 participants aged 8 to 20 years with a BMI ≥ 18.5 kg/m2. Serum vitamin D levels were categorized as deficient (<20 ng/mL), insufficiency (20-30 ng/mL), and sufficient (≥30 ng/mL). The ASMI was calculated as appendicular skeletal muscle mass divided by height squared (kg/m2). Multivariable linear regression models adjusted for age, sex, race, education, blood pressure, dietary factors, and physical activity were employed to assess the association. The dose-response relationship between vitamin D and ASMI was analyzed using generalized additive models and fitted curves. Stratified analyses by sex were conducted to evaluate potential effect modifications. A significant negative correlation was observed between vitamin D level and ASMI. For every 1 ng/mL increase in vitamin D, ASMI decreased by 0.02 kg/m2 (P < .0001). This study highlights a negative association between vitamin D levels and ASMI in adolescents in the US with a BMI ≥ 18.5 kg/m2.